This invention is concerned with a method for sealing containers which are capable of being closed and which contain flowable compositions and is concerned also with a container assembly which includes a flowable composition and an improved seal therefor. More particularly, this invention relates to a method for establishing a sealing layer in a container for a flowable composition by application of material which causes the reaction of the flowable composition, whereby a protective coating is formed and to the resulting container assembly.
The storage and transport, as well as warehousing of reactive flowable compositions, such as compositions which may react in the presence of air or moisture, generally present no difficulties for a consumer, providing the compositions are contained in completely closed containers and the compositions in the containers may be partially used without substantial destruction of the remaining material. Generally, however, once the container of a composition which is sensitive to air or moisture has been opened, its contents must be used up at once.
Frequently, a consumer desires to use only part of the composition held in a container and it is desirable, particularly for moisture or air sensitive flowable compositions, to have a container which is closed in such a manner that the flowable composition does not become worthless after a single use. If for no other reason than cost, containers which are intended to hold materials such as adhesive compositions, paints, and the like for mass consumption cannot be expected to meet exact specifications for seal tightness as in the case, for example, of precision instruments.
Cartridges, which are used on a large scale in the engineering area and for home maintenance and which contain, for example, adhesive material such as mortar compositions, catalysts, etc., are particularly characteristic containers for flowable compositions which are sensitive to air or moisture. The cartridges generally have a hollow, cylindrical body into which plunges a piston which is capable of forcing the flowable composition out of the opposite end; the piston also has a sealing function. Such cartridges are intended for compositions which will be consumed only partially after each use. To apply the flowable composition, the piston is advanced in the cartridge and the corresponding amount of flowable composition is supplied to the desired area, usually through a spout-like or nozzle outlet on the opposite face of the cartridge.
For reasons of manufacture, the pistons of such known cartridges have a certain play within the cartridges and for ease of use, must have a certain play so that the frictional resistance does not become excessive. As a consequence, air can enter the flowable, viscous composition through the gap between the piston and the inner wall of the cartridge; eventually, due to the action of air and/or moisture, the contents of the cartridge usually become useless. In addition, the composition can flow to the outside through this gap.
The caulking tube disclosed by Robillard in U.S. Pat. No. 4,217,995, which is incorporated herein by reference, is an example of a container for a flowable composition which is sensitive to air and/or moisture, wherein the container is comprised of a cartridge and a piston. To seal the caulking tube against air and moisture, a moisture proof material such as polyethylene wax is coated on the inner surface of the rear end of the cartridge. This method of sealing a container for a flowable composition has not been found completely satisfactory.
Attempts to remedy problems of cartridge-piston type containers by means of sealing lips on the piston have also not led to satisfactory results. Either due to manufacturing tolerances, or the aging phenomena of the plastic used for the cartridge and/or piston, including shrinkage and embrittlement, the seal becomes unsatisfactory or frictional resistances are unreasonably high from a processing point of view.